Recently, next-generation nonvolatile memory devices having good operation characteristics and improved integration of elements have become a matter of increasing concern. Research for a ferroelectric RAM (FRAM), which includes memory cells each having a pair of electrodes and a ferroelectric material interposed between the electrodes, among such next-generation nonvolatile memory devices has been actively performed.
FRAM receives an input of a signal through an adjustment of a polarization direction as an electric field is applied between a pair of electrodes, and stores digital signals “1” and “0” in accordance with the direction of residual polarization remaining after the electric field is removed. FRAM has characteristics of low power consumption, excellent durability, rapid operation speed, low driving voltage, and the like.
Generally, a pair of electrodes of an FRAM is formed by depositing a conductive material on a substrate using an evaporation method or a sputtering method.
Also, as the ferroelectric material interposed between a pair of electrodes, an inorganic material capable of exhibiting ferroelectricity, such as PbZrxTi1-xO3 (PZT), SrBi2O9 (SBT), and (Bi, La)4Ti3O12 (BLT), has been used.